The present invention relates to an image reading method for reading images recorded on a transparent-type original such as a negative film, a reversal film or the like. In particular, the present invention relates to an image reading method which is able to read images with high accuracy to thereby obtain reproduced images of high quality regardless of whether the transparent-type originals is a negative film or a reversal film.
In recent years, there has been developed a digital photoprinter which reads photoelectrically image information recorded on a photographic film such as negative film, a reversal film or the like, converts the read images into digital signals, performs various image processing operations on the digital signals to thereby provide image information for recording, and scans and exposes a photosensitive material such as photographic paper or the like by means of a recording light modulated according to the image information to thereby provide a print.
The digital photoprinter is able to carry out freely editing and layout operations on print images such as synthesis of a plurality of images, division of an image or the like, editing of characters and images, and other similar editing, and is also able to perform various image processing operations such as color/density adjustment, scaling, outline emphasis and the like. That is, the digital photoprinter is able to freely edit images and perform processing on the images according to their uses to thereby provide a finished print.
In a print obtained by a conventional a real exposure, in terms of density resolution, spatial resolution, color/density reproduction and the like, all of the image information recorded on the film cannot be reproduced. On the other hand, in a digital photoprinter, it is possible to output a print in which almost 100% of image density information recorded on a film is reproduced.
The digital photoprinter includes as basic components a reading device for reading images recorded on an original such as a film or the like, a set-up device for performing processing on the read images and determining exposure conditions in the following step, and an image forming device for scanning and exposing a photosensitive material in accordance with the determined exposure conditions to thereby perform development processing on the photosensitive material.
In an image reading device that reads images recorded on a film or the like, for example, in the case of reading according to slit scanning, a slit-like reading light beam extending in a one-dimensional direction is radiated onto the film and, at the same time, the film is moved in a direction substantially perpendicularly intersecting the above-mentioned one-dimensional direction (or the reading light and photoelectric transducer device are moved), whereby the film is scanned by use of the reading light in a two-dimensional manner.
The transmitted light carrying the film image that has passed through the film is formed into an image on the light receiving surface of a photoelectric transducer device such as a CCD line sensor or the like, converted photoelectrically, and then further processed as the situation requires.
The light quantity data that is read is then amplified and A/D converted into a digital signal. Subsequently, the digital signal undergoes various image processing operations such as correction of characteristic variations by the respective CCD elements, density change, scaling and the like. Next, the digital signal is transferred to the set-up device.
The set-up device reproduces the image information transferred thereto on a display such as a CRT or the like as a visible image.
On viewing the reproduced image, an operator performs further additional correction processing operations such as gradation correction processing, color/density correction processing and the like on the reproduced image (setting of the set-up conditions) and, if the operator judges that the reproduced image is satisfactory as a finished print, then the reproduced image is transferred to the image forming device as the image information for recording.
In this image forming device, if the image information requires the use of image recording by means of raster scanning (light beam scanning), then three light beams respectively corresponding to three primary color photosensitive layers formed in a photosensitive material, for example, corresponding to R(red), G(green), and B(blue) exposures, are respectively modulated according to the image information for recording, so that they are deflected in a main scan direction (which corresponds to the above-mentioned one-dimensional direction). Also, by sub-scanning and carrying the photosensitive material in a direction substantially perpendicularly intersecting the main scan direction (by sub-scanning the deflected light beams and photosensitive material relatively to each other), the photosensitive material is scanned and exposed in a two-dimensional manner by the light beams modulated according to the recording images, so that the film image is recorded on the photosensitive material.
Subsequently, the exposed photosensitive material undergoes developing processing according to the type of the photosensitive material, for example, if it is a silver salt photographic photosensitive material, then a developing processing comprising color development, bleach-fix, washing, drying and the like are performed on the silver salt photosensitive material, and then it is output as a finished print.
As is known well, a film is not always exposed to a proper quantity of light, and sometimes suffers from various exposures, for example, it may be underexposed or overexposed. Referring to an image density D(=log E) recorded on a normal negative film, the maximum density thereof is of the order of 2.8-3.2, whereas the maximum density of an image to be recorded on a normal reversal film reaches the order of 3.2-3.8.
In order to obtain a finished print of high quality in a digital photoprinter, it is necessary to use a photoelectric transducer device which has not only a higher spatial resolution but also a higher density (quantity of light) resolution, for example, it is preferred to use a CCD or the like. However, in general, a photoelectric transducer having both higher spatial and density resolutions provides a narrow measurable density range (dynamic range), and thus such conversion elements make it difficult to measure the whole density range of a negative or reversal film.
Therefore, in an image reading device for use in a digital photoprinter or the like, to set a density range which can be read by the photoelectric transducer, before a film image is read for printing, the image reading device performs a pre-reading operation (a prescanning), in which a film image is coarsely read while the measuring density area of the photoelectric transducer is set wide, thereby setting an image reading density range in an image reading operation (a main scanning) for output to a finished print.
In main scanning, the reading of a transmitted light by the photoelectric transducer is adjusted according to the set image reading density range, that is, an offset density is applied to the transmitted light reading by the photoelectric transducer to thereby adjust (reduce) the reading density range. In an offset density application method, the quantity of light of a reading light source can be adjusted (adjustment of a reading light), the quantity of light of the transmitted light can be adjusted, or the gain of an amplifier can be changed, and, if the photoelectric transducer is a CCD, then the storage time can be changed. That is, various methods are available.
It should be noted that a negative film and a reversal film differ greatly in image characteristics from each other. That is, an image recorded on a negative-film is not to be viewed directly but is printed on paper before it can be viewed normally. For this reason, the image is usually printed on printing paper by means of LATD (large area transmittance density). On the other hand, an image recorded on a reversal film is to be viewed directly.
The developing characteristics of the three primary colors, that is, R, G and B of the negative and reversal films, are respectively designed according to their respective uses. That is, the negative film is designed so that an image of higher quality can be obtained when it is printed on the printing paper, whereas the reversal film is designed so that the recorded image itself is of higher quality.
Therefore, if the same offset density is employed for both negative film and reversal film differing entirely in characteristics from each other in the main scanning (image reading), then color balance is lost or other problems are incurred. To achieve a highly accurate image reading operation to thereby obtain a finished print of higher image quality, different offset densities may be preferably applied according to the type of film, that is, according to whether the film is a negative film or a reversal film.
However, in the conventional method of reading transparent-type originals, when a reversal film is read, the only adjustment carried out is the insertion of a filter corresponding to the lowest image density (mask density) of the negative film in order to match the lowest image density of the reversal film to the negative film. Due to this, white balance is lost in the image reading, which results in a problem that the quality of the reproduced image is reduced.